From a viewpoint of efficient use of an air conditioner, which is caused by the problem of environmental pollution or an increase of power saving tastes, a need for restricting ventilation in a room has recently grown. In such a case where ventilation is restricted in a space in which restriction of the ventilation is possible, respiration of a person causes a decrease of an oxygen concentration and an increase of a carbon dioxide concentration in an air.
Here, particularly, it is important to maintain the carbon dioxide concentration to be an adequate value in a space in which a person exists. This is because a rate at which the carbon dioxide concentration in the air increases up to a value harmful to a human body is faster than a rate at which the oxygen concentration decreases up to a value harmful to the human body in a space in which ventilation is restricted.
For example, in a case where one person exists in a vehicle in which ventilation is restricted, a period when the oxygen concentration decreases from a value (about 21%) thereof in the air to a value (18%) stated as limit for safety is about 5 hours. However, a period when the carbon dioxide concentration increases from a value (about 400 ppm) thereof in the air to a value (3000 ppm) stated as that health may be adversely affected is about 30 minutes. That is, the period when the carbon dioxide concentration increases is significantly short.
Thus, it is important to suppress an increase of the carbon dioxide concentration in a space where a person exists. A technology of removing carbon dioxide in the air has been developed in order to suppress the increase of the carbon dioxide concentration. For example, PTL 1 discloses a technology in which carbon dioxide in an air is absorbed and removed by using an absorbent which has an amine-based organic substance attached thereto. PTL 2 discloses a technology in which carbon dioxide in an air is absorbed and removed by using activated carbon.